Liquids and Solids

Relative Magnitudes of Forces The types of bonding forces vary in their strength as measured by average bond energy. Covalent bonds (400 kcal/mol) Hydrogen bonding (12-16 kcal/mol ) Dipole-dipole interactions (2-0.5 kcal/mol) London forces (less than 1 kcal/mol) Strongest Weakest

Hydrogen Bonding Bonding between hydrogen and more electronegative neighboring atoms such as oxygen and nitrogen Hydrogen bonding between ammonia and water

Hydrogen Bonding in DNA TA Thymine hydrogen bonds to Adenine

Hydrogen Bonding in DNA CG Cytosine hydrogen bonds to Guanine

London Dispersion Forces The temporary separations of charge that lead to the London force attractions are what attract one nonpolar molecule to its neighbors. Fritz London London forces increase with the size of the molecules.

London Dispersion Forces

London Forces in Hydrocarbons

Boiling point as a measure of intermolecular attractive forces

Some Properties of a Liquid  Surface Tension: The resistance to an increase in its surface area (polar molecules, liquid metals).  Capillary Action: Spontaneous rising of a liquid in a narrow tube.

Some Properties of a Liquid  Viscosity: Resistance to flow  High viscosity is an indication of strong indication of strong intermolecular forces intermolecular forces

Types of Solids  Crystalline Solids: highly regular arrangement of their components

Types of Solids  Amorphous solids: considerable disorder in their structures (glass).

Representation of Components in a Crystalline Solid Lattice: A 3-dimensional system of points designating the centers of components (atoms, ions, or molecules) that make up the substance.

Bragg’s Law xy + yz = n and xy + yz = 2d sin   n = 2d sin 

Crystal Structures - Cubic Simple Face-Centered Body-Centered

Crystal Structures - Monoclinic Simple End Face-Centered

Crystal Structures - Tetragonal Simple Body-Centered

Crystal Structures - Orthorhombic SimpleEndFace-CenteredBodyCenteredFaceCentered

Crystal Structures – Other Shapes Rhombohedral Triclinic Hexagonal

Packing in Metals Model: Packing uniform, hard spheres to best use available space. This is called closest packing. Each atom has 12 nearest neighbors.

Closest Packing Holes

Metal Alloys  Substitutional Alloy: some metal atoms replaced by others of similar size. brass = Cu/Znbrass = Cu/Zn

Metal Alloys (continued)  Interstitial Alloy: Interstices (holes) in closest packed metal structure are occupied by small atoms. steel = iron + carbonsteel = iron + carbon

Network Atomic Solids Some covalently bonded substances DO NOT form discrete molecules. Diamond, a network of covalently bonded carbon atoms Graphite, a network of covalently bonded carbon atoms

Molecular Solids Strong covalent forces within molecules Weak covalent forces between molecules Sulfur, S 8 Phosphorus, P 4

Equilibrium Vapor Pressure  The pressure of the vapor present at equilibrium.  Determined principally by the size of the intermolecular forces in the liquid.  Increases significantly with temperature.  Volatile liquids have high vapor pressures.

Water phase changes Temperature remains __________ during a phase change. constant Energy

Phase Diagram  Represents phases as a function of temperature and pressure.  Critical temperature: temperature above which the vapor can not be liquefied.  Critical pressure: pressure required to liquefy AT the critical temperature.  Critical point: critical temperature and pressure (for water, T c = 374°C and 218 atm).

Phase changes by Name

Water

Carbon dioxide

Carbon

Sulfur